Fine algae culture device

ABSTRACT

This invention relates to a culture device of a domed shape, a conical shape, or a cylindrical shape of a closed type used for culture of microalgae, and a gas discharge device set so as to be movable in the culture device. The culture device is basically composed of a transparent inside member (a semispherical dome, a conical peripheral wall, or a cylindrical peripheral wall), a transparent outside member, and a bottom portion connecting the lower ends of the two members, a cylindrical opening portion is provided at the top part of the outside member, and a gas introducing member and a discharging member of a culture solution are provided in the bottom portion. The gas discharge device is basically composed of two opposed rectangular base plates, a bubble guide member, and a discharge nozzle. The culture solution can be agitated without mechanical agitation and the culture can be carried out in high concentrations.

TECHNICAL FIELD

The present invention relates to a culture device of a domed shape, aconical shape, or a cylindrical shape used in culture of photosyntheticorganisms such as microalgae or the like, a gas discharge devicedisposed so as to be movable in the culture device and functioning tosupply gas necessary for the culture into a culture solution and agitatethe culture solution, or a culture system as a combination of theculture device with the gas discharge device.

BACKGROUND ART

In order to produce useful substances such as vitamins, amino acids,pigments, proteins, polysaccharides, fatty acids, and so on or in orderto dispose of carbon dioxide which is considered to be one of causes ofglobal warming, extensive research has been conducted heretofore on massculture of microorganisms including microalgae such as Chlorella,Spirulina, or the like, and products of cultures based on the result ofresearch are commercially available.

Most of the algae among these microorganisms absorb carbon dioxide tobiosynthesize the useful substances by photosynthesis. In this case,because it is important to effect the culture of algae efficiently, aculture apparatus for making the algae efficiently perform thephotosynthesis is necessary. Therefore, improvement in the conventionalculture apparatus and development of new culture apparatus are underway.

The conventional algae culture apparatus commonly known include, forexample, culture ponds, raceway culture devices, tubular culturedevices, liquid membrane forming culture devices, and so on. Theartificial culture ponds are of a type in which a culture pool or aculture tank is constructed, for example, of concrete outdoors, theculture solution is poured into the pool to form a culture pond, and themicroalgae such as Chlorella or the like are cultured in the solution bymaking use of the sunlight. However, the systems of this typenecessitate the surface area of the pool, for example, of 3000 M² andare thus normally huge.

In addition, when the microalgae are cultured in the system of thistype, concentrations of the microalgae increase in the culture solutionwith progress of culture, so as to turn the solution into deep green andthus inhibit the sunlight from reaching the bottom part of the culturepond. From this phenomenon, there will arise a problem that the overallefficiency of photosynthesis of algae is decreased, unless the cultureconcentrations of the microalgae are lowered.

For this reason, the depth of the solution has to be kept below 15 cmand broad areas are necessary for the volume culture of microalgae.Since the concentrations of the culture solution cannot be high, therearises a problem that, for collecting the cultures from the solution,the cultures must be collected from an enormous amount of the culturesolution with low concentration.

On the other hand, the culture ponds have to be agitated to facilitatethe photosynthesis of the microalgae, but a lot of energy is necessaryfor agitating the huge amount of the solution of low concentration.Further, because the culture ponds are set outdoors and are open to theair, impurities of dirt, dust, etc. are mixed readily into the solution,and microorganisms and other algae floating in the air are mixed intothe ponds to propagate; these pose another problem that the culturescannot be obtained in high purity and with high quality.

Since the culture ponds are set outdoors, the temperature varies withvariations in climate and it is thus very difficult to keep thetemperature of the ponds constant. Particularly, the culture ponds havesuch a drawback that the temperature becomes too low in the winterseason, depending upon regions.

For these reasons, the culture of algae making use of the culture pondshas such a drawback that it cannot be applied to the algae except forthose such as Chlorella, Spirulina, and Dunaliella which can grow evenunder such a special condition as high pH or high salinity.

The raceway culture apparatus is constructed in such structure that theinside of a culture tank is partitioned with straightening plates toform a circuit path of the culture solution and the algae are cultivatedby a method for circulating the culture solution in the circuit path bycirculating means. This method is an improvement in the method of theculture ponds, but it also fails to utilize the light efficiently,because rates of photosynthesis of algae are lowered with progress ofthe culture, as in the case of the culture method with the cultureponds. This also raises a problem of low utilization efficiency ofcarbonic acid gas. For accomplishing efficient utilization of light,there is also a suggestion of guiding the sunlight through opticalfibers into the solution. (Japanese Laid-open Utility Model ApplicationNo. 5-43900)

However, since the solution is circulated by mechanical agitation in thecase of the culture of algae by this method, this method will encountersuch an inevitable drawback that cells of algae are subject to breakageor shear stress (a phenomenon in which the algae are cut by shearingstress to degrade the activity of cells and thus make growth ratesslower).

The tubular culture apparatus is an apparatus for culturing themicroalgae etc. by use of the culture tank constructed of alight-transmitting tube. When the algae are cultured by use of thisapparatus, there is no contamination of the culture solution due tovarious germs or the like and the culture concentrations can also behigh; therefore, this is an extremely advantageous method for separatingthe algae from the culture solution and collecting the useful substancesproduced by the algae.

However, after long-term culture of algae, the algae attach to theinternal wall of the tube, so as to considerably decrease the quantityof light transmitted by the tube. This phenomenon makes the efficientculture of microalgae difficult and it is not easy to remove the algaeattaching to the internal wall of the tube.

For solving this problem, there is a suggestion about a method forputting cleaning balls in the tube and always circulating these ballswith the culture solution, thereby cleaning the internal wall of thetube (Japanese Laid-open Patent Application No. 6-90739). This method,however, has many problems; it is not possible to continuously removethe dirt and the attachment of algae on the internal wall of the tubewell, the balls have to be collected and cleaned, the balls always haveto be circulated in the tube, and so on. A further problem of theculture of algae according to this method is that oxygen gas resultingfrom the photosynthesis of algae stays inside the tube because of theculture inside the tube and this oxygen acts to inhibit thephotosynthesis of algae conversely (inhibition of photosynthesis). Thereis thus another suggestion about an idea of a device for suppressing theadverse effect on the culture due to the oxygen evolving in thephotosynthesis. (Japanese Laid-open Patent Application No. 9-121835)

The liquid film forming culture apparatus is one constructed in suchstructure that a light-transmitting domed lid is placed on the culturetank, the culture solution is sprayed from below toward the internalsurface at the top of the domed lid to form a liquid film of the culturesolution on the internal surface of the lid, and this liquid film isexposed to the light. (Japanese Laid-open Patent Application No.8-38159)

This suggested method, however, has problems that it requires acirculating pump for continuously forming the liquid film, that it isnot suitable for the mass culture, that the sunlight cannot be utilized,and so on.

Since the microalgae accumulate the useful substances in their bodythrough the photosynthesis, a significant challenge is to make themicroalgae conduct the photosynthesis at as high efficiency as possible.Conceivable factors for the efficient photosynthesis are enlargement ofthe light-receiving area of the culture apparatus, efficient agitationof the culture solution, adjustment of the thickness or the depth of theculture solution, easiness of cleaning to remove the microalgaeattaching to the internal surface of the culture apparatus, control oftemperature, prevention of mixture of foreign germs, other microalgae,and impurities, and so on.

The issue of the light-receiving area is influenced by how large thelight-receiving area is or by how efficiently the culture solution isexposed to the light.

For example, in the case of the culture tanks or the culture ponds, thesurface area is determined by the surface of the culture tanks or theculture ponds; therefore, the enlargement of the surface area can beachieved only by increasing the size of the tanks or the ponds and thereis no alternative means.

The agitation of the culture solution is essential to uniformirradiation of light to the culture solution and an ordinary meanstherefor is often agitation or movement of the solution, for example, bya pump, or mechanical agitation in the tanks, the ponds, and so on.

Such mechanical agitation, however, is not preferable, because it causesbreakage or shear stress of cells of microalgae.

Since photosynthesis rates differ depending upon kinds of microalgae, itis necessary to employ different depths of the culture solution betweenalgae of low rates and algae of high rates. It is also necessary tochange the depth according to an expected culture concentration. Asdescribed, the thickness or depth of the culture solution needs to befreely adjusted according to the conditions including the kind ofmicroalgae, the expected culture concentration, and so on.

The removal and cleaning of the microalgae attaching to the internalsurface of the culture apparatus is not so significant in the case ofthe open type culture ponds and culture tanks set outdoors. This removaland cleaning is, however, essential to the culture apparatus of theclosed type, because the attaching microalgae come to intercept thelight. In addition, the apparatus needs to be constructed in suchstructure that at the stage of completion of the culture the insidesurface of the apparatus can be cleaned for the next culture, so as toremove the attachments readily.

The temperature control is very important, particularly, for the closedtype apparatus, because the temperature of the solution becomes too highin the summer season and causes a trouble in the culture. One ofsolutions to it is a method for mixing cool water into the culturesolution, but, because of dilution of the culture solution, a largeamount of the culture solution thus diluted has to be dealt with in thenext step of collection of the cultured algae. This method is,therefore, very disadvantageous from the industrial aspect.

The culture devices are normally either those for outdoor use or thosefor indoor use. Therefore, if the devices for outdoor use are usedindoors, there will arise a problem that the efficiency of utilizationof light is low; on the other hand, there also arises a problem that thedevices for indoor use cannot be used outdoors. There are thusincreasing demands for the culture apparatus of simple structure thatpermits the culture under ordinary culture conditions both indoors andoutdoors.

The agitation of the culture solution is an essential operation touniform culture. The reason is that it is carried out for the followingpurposes; (1) to cancel the difference of culture rates appearingbetween the surface layer part and the deep layer part of the liquidmedium; (2) to uniformly distribute the gas such as air, carbon dioxide,or the like across the whole of the liquid medium or the culturesolution; (3) to uniformly distribute the light over the microalgae tobe cultured; (4) to prevent the microalgae likely to form coloniesduring the culture from settling and depositing in the liquid bottompart and to make them re-scattered in the culture solution; and so on.

It is thus necessary to always agitate the culture solution and tosupply the necessary air or carbonic acid gas or the like into theculture solution.

An object of the present invention is, therefore, to provide a closedtype culture device of microalgae as a culture device overcoming thedrawbacks of the conventional open type or closed type culture devices,of which the shape is domed, conical, or cylindrical and which has theadvantages including the following: (1) the foreign germs and impuritiesare prevented from being mixed in the device; (2) the temperaturecontrol of the culture solution is easy; (3) the solution can beagitated without mechanical agitation of the culture solution, so as toprevent the cells of algae from being broken and prevent the shearstress from appearing; (4) the culture concentrations can be set high;(5) the cleaning of the device is easy; (6) the culture is not inhibitedby the evolving oxygen; and (7) the efficiency of utilization of lightis high.

Another object of the present invention is to provide a gas dischargedevice used in the culture device, which has advantages including thefollowing; when the necessary gas is supplied into the culture solutionby use of this device, the device undergoes movement to agitate thesolution and the solution is also agitated by the discharged gas,whereby contact is extremely good between the supplied gas and theculture solution, thereby increasing the culture efficiency.

Further, the present invention relates to a culture apparatuscharacterized by a combination of the above-stated culture device withthe above-stated gas discharge device.

DISCLOSURE OF THE INVENTION

A culture device of microalgae according to the present invention is aculture device of either shape selected from a domed shape, a conicalshape, and a cylindrical shape; the culture device of the domed shape isa culture device of a domed shape comprising an outside semisphericaldome of a transparent material, an inside semispherical dome of atransparent material, and a bottom portion connecting lower ends of thetwo domes, wherein a cylindrical opening portion is provided at top partof the outside semispherical dome, and an introducing member of airand/or carbonic acid gas and a discharging member of a culture solutionare provided in the bottom portion, and wherein a member for watersprinkling is provided outside the cylindrical opening portion and asprinkled water receiver is provided around the outside periphery of thebottom portion as occasion may demand;

the culture device of the conical shape is a device comprising anoutside conical peripheral wall of a transparent material, an insideconical peripheral wall of a transparent material, and a bottom portionconnecting lower ends of the two peripheral walls, wherein a cylindricalopening portion is provided at top part of the outside conicalperipheral wall, and an introducing member of air and/or carbonic acidgas and a discharging member of a culture solution are provided in thebottom portion, and wherein a member for water sprinkling is providedoutside the cylindrical opening portion and a sprinkled water receiveris provided around the outside periphery of the bottom portion asoccasion may demand;

the culture device of the cylindrical shape is a device comprising anoutside cylindrical peripheral wall having an upper wall of atransparent material, an inside cylindrical peripheral wall having anupper wall of a transparent material, and a bottom portion connectinglower ends of the two peripheral walls, wherein a cylindrical openingportion is provided in central part of the upper wall of the outsidecylindrical peripheral wall, and an introducing member of air and/orcarbonic acid gas and a discharging member of a culture solution areprovided in the bottom portion, and wherein a water sprinkling member isprovided outside the cylindrical opening portion and a sprinkled waterreceiver is provided around the outside periphery of the bottom portionas occasion may demand.

A gas discharge device for use in the culture device of microalgae is adevice comprising two opposed rectangular base plates, a bubble guidemember of a U-shaped cross section or an inverted-U-shaped cross sectionopening down, and a discharge nozzle, wherein the bubble guide member isset as inclined with respect to upper surfaces of the rectangular baseplates, an inclined wall as an upper surface thereof is bent at an upperend thereof to form an upper wall extending substantially horizontally,the bubble guide member has side walls hanging down from the both sideedges of the inclined wall and upper wall, and lower ends of the twoside walls are joined to the upper surfaces of the rectangular baseplates,

wherein the discharge nozzle is set through a through hole bored in alower portion of the inclined wall so as to be rotatable, wherein atleast one of the opposed rectangular base plates is bent in the samedirection at a front end portion and/or at a rear end portion asoccasion may demand, or wherein at least one of the rectangular baseplates is provided with weight adjusting means.

Further, the present invention is a culture apparatus as a combinationof the aforementioned culture device with the above gas dischargedevice.

The transparent material used in the culture devices can be anytransparent material as long as it is excellent in thelight-transmitting property and has sufficient weather resistance andresistance to ultraviolet rays; for example, it can be selected frommaterials such as acrylic resin, polycarbonate, polypropylene,polyethylene, polyvinyl chloride, glass, and so on; the synthetic resincan be suitably applicable in terms of ease to work; particularly, theacrylic resin is a most preferable material, because it has theaforementioned characteristics.

The gas introduced into the culture device must contain carbonic acidgas in its components and may be one with an increased concentration ofcarbonic acid gas by mixing carbonic acid gas in air; the air andcarbonic acid gas may also be introduced separately into the device.

The carbonic acid gas is most preferably used in the form of a mixturewith air. While an air bubble containing carbonic acid gas rises to thesurface with agitating the culture solution, the carbonic acid gas isdispersed and absorbed in the culture solution and the air functions toremove oxygen evolving in the culture from the culture solution. If thecarbonic acid gas is introduced alone into the culture solutionintroducing rates of carbonic acid gas will be low and dispersing ratesof carbonic acid gas into the culture solution will tend to become slowinevitably.

The cylindrical opening portion works to exhaust the air introduced intothe culture solution, unused carbonic acid gas, and evolving oxygen intothe atmosphere; however, if the opening portion is open to theatmosphere, the impurities of dust etc. will enter the device. In orderto prevent the mixture of such substances, it is preferable to providethe opening portion with a filter member or to provide the openingportion with such a lid member as to act in similar fashion to thefilter member.

This opening portion may be molded in an integral form with the outsidesemispherical dome, the outside conical peripheral wall, or the upperwall of the outside cylindrical peripheral wall or may be one moldedseparately and fixed thereto.

The culture device of the domed shape, the conical shape, or thecylindrical shape used as a culture device body can be constructed ineither of the following ways; each of the outside member and insidemember is formed integrally; one of them is formed integrally while theother as an assembly of properly divided members of two parts or of fourparts; the both members may be assemblies of divided members. The way ofmaking the device can be determined according to the size and shape ofthe culture device.

Further, the material and structure of the sprinkled water receiver canbe determined arbitrarily as long as the member can receive waterstreams sprinkled over and flowing down on the outside surface of thedevice. The material can be either a metal material or a plasticmaterial.

The structure of the sprinkled water receiver can be either of thefollowing; it is molded as a separate member from the culture devicebody; the receiver is constructed by extending the lower end of theoutside member of the culture device horizontally around the outsideperiphery and bending the end portion upward; the sprinkled waterreceiver is constructed by extending the lower end of the inside memberof the culture device horizontally around the outside periphery andbending the end portion upward.

A preferred configuration of the sprinkled water receiver is a membermolded as a separate member from the culture device body.

The introducing member of air and/or carbonic acid gas provided in thebottom portion can be a tubular member having a lot of gas dischargeports, or gas discharge ports perforated in the bottom portion.

Since the gas introduced from this introducing member into the culturesolution agitates the culture solution with moving up in the culturesolution, the culture solution does not have to be mechanically agitatedintentionally. This method can prevent the breakage of cells and theoccurrence of shear stress due to the mechanical agitation accordingly.

The oxygen gas evolving in the photosynthesis can be dischargedefficiently and quickly from the culture solution with the ascent of thegas.

There are two methods for supplying the culture solution into theculture device. The first method is a method for providing the bottomportion with a supply member (for example, a supply hole bored in thebottom portion) and supplying the culture solution through this supplymember.

The second method is a method for supplying the culture solution throughthe cylindrical opening portion at the top part.

Provision of various supply and introducing members in the device willcause complication of the device and also have a problem ofcontamination on the occasion of change of the kind of microalgae to becultured.

Therefore, the second method is most preferable.

Since the outside member and the inside member of the culture deviceboth are made of the transparent material, if an artificial light sourceis provided in the inside space of the culture device the culture canalso be carried out during the nighttime in the case of the outdoorculture. In the case of the indoor culture, efficient, continuousculture can be realized with two artificial light sources set inside andoutside the culture device.

Since the culture device of the domed shape has a small occupying areabut a large surface area, the light-receiving area thereof is large. Inthis device agitation of the culture solution is effected extremelywell. When this device is made of a plastic material, it can be formedreadily by vacuum forming and thus can be made at the lowest cost.

For these reasons, the culture device of the domed shape is mostpreferable as a microalgae culture device.

It is preferable to provide the culture device with various sensors suchas a temperature sensor, a liquid level sensor, a pH sensor, a dissolvedoxygen amount sensor, or the like for controlling and monitoring theculture conditions. These sensors are set through the cylindricalopening portion or through the outside wall of the device.

Since the gas discharge device of the present invention discharges thegas of air or the like obliquely downwardly toward the bottom portion ofthe culture device, it advances as hopping like a frog in the device.This motion causes the culture solution to be agitated hard and thedischarged gas also agitates the culture solution during the ascent inthe culture solution. Particularly, in cases where the microalgae to becultured are likely to form colonies, the gas discharged from the gasdischarge device breaks the colonies and disperses the microalgae in theculture solution, thereby increasing the culture efficiency.

The gas discharge device is normally made of a plastic material and isprovided with the weight adjusting means to adjust the weight of thedevice.

The microalgae that can be cultured by the use of the culture device ofthe present invention include a variety of microalgae, in addition toChlorella, Spirulina, and Dunaliella commercially successful heretofore.For example, such microalgae include those with excellent values addedthat produce useful substances, such as Haematococcus pluviarisproducing β-ketocarotenoid (astaxanthin), Isochrysis galbana (Isocrysisgalvana) being used as live bait for cultivation of marine fishes orproducing a highly unsaturated fatty acid (DHA), Nannochloropsis oculataalso being used as live bait for cultivation of marine fishes orproducing a highly unsaturated fatty acid (EPA), and so on. The cultureapparatus of the present invention can culture these microalgae in highconcentrations and at high utilization efficiency of light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a culture device of the domed shapeaccording to the present invention;

FIG. 2 is a partial, schematic view to show a state during the culturein the culture device of the domed shape illustrated in FIG. 1;

FIG. 3 is a front view of the culture device of the domed shapeillustrated in FIG. 1;

FIG. 4 is an explanatory diagram to show a mass culture system ofmicroalgae utilizing the culture devices of the domed shape illustratedin FIG. 1 to FIG. 3;

FIG. 5 is a sectional view of a culture device of the conical shapeaccording to the present invention;

FIG. 6 is a front view of the culture device of the conical shape ofFIG. 5;

FIG. 7 is a sectional view of a culture device of the cylindrical shapeaccording to the present invention;

FIG. 8 is a front view of the culture device of the cylindrical shape ofFIG. 7;

FIG. 9 is a perspective view of a gas discharge device;

FIG. 10 is a side view of the gas discharge device of FIG. 9;

FIG. 11 is a plan view of the gas discharge device of FIG. 9;

FIG. 12 is a sectional view of the gas discharge device of FIG. 9;

FIG. 13 is an enlarged sectional view of a discharge nozzle of the gasdischarge device of FIG. 9;

FIG. 14 is a sectional, explanatory drawing to show a state in which thegas discharge device is discharging the gas into the culture solution;

FIG. 15 is a sectional, explanatory drawing of a culture apparatus as acombination of the culture device of the domed shape itself with the gasdischarge device;

FIG. 16 is a top plan view, partly broken, of FIG. 15;

FIG. 17 is a sectional, explanatory drawing of a culture apparatus as acombination of the culture device of the conical shape itself with thegas discharge device;

FIG. 18 is a sectional, explanatory drawing of a culture apparatus as acombination of the culture device of the cylindrical shape itself withthe gas discharge device;

FIG. 19 is a perspective view to show another example of the gasdischarge device of the present invention;

FIG. 20 is a perspective view to show a further example of the gasdischarge device of the present invention;

FIG. 21 is a perspective view to show yet another example of the gasdischarge device of the present invention; and

FIG. 22 is a sectional view along the line X-X′ in FIG. 21.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to explain the present invention in more detail, the culturedevices and gas discharge devices according to the present inventionwill be described with reference to the accompanying drawings.

FIG. 1 to FIG. 3 show the culture device 1 of the domed shape.

FIG. 3 is a front view of the culture device 1 of the domed shape, inwhich a cylindrical opening portion 4 is provided at the top part ofoutside semispherical dome 8, a water sprinkling member 3 for coolingthe dome 8 is provided outside the cylindrical opening portion 4, asprinkled water receiver 11 for receiving the water sprinkled from thesprinkling member 3 is provided at the lower part of the dome 8, and thedevice 1 is supported by a plurality of fixing members 16. A gasintroducing member 6 and a discharging member 7 of the culture solutionare attached to a bottom portion 14 of the culture device.

FIG. 1 is a sectional view of the device 1. This device 1 is constructedof the outside semispherical dome 8, an inside semispherical dome 9, andthe bottom portion 14 for connecting the lower ends of the two domes.The cylindrical opening portion 4 is provided as a separate member atthe top part of the dome 8, and the water sprinkling member 3 isprovided outside the cylindrical opening portion 4, so that coolingwater 15 is sprinkled from this water sprinkling member 3 over thesurface of the dome 8 and drops with covering the surface of the dome 8in the film form down to the sprinkled water receiver 11.

The temperature of the culture solution 5 is controlled by this coolingwater 15 (see FIG. 2).

Each of the dome 8, dome 9, bottom portion 14, cylindrical openingportion 4, and sprinkled water receiver 11 is made of a transparentmaterial. The transparent material used herein is the acrylic resin. Ametallic material such as stainless steel or the like can also bepreferably employed as a material for the sprinkled water receiver 11.The cooling water is drained off from the sprinkled water receiver 11through a drain member (not illustrated). The water thus drained isstored and then is again used as cooling water.

Attached to the bottom portion 14 are the gas introducing member 6 forsupplying air and/or carbonic acid gas into the culture solution 5 andthe discharging member 7 for discharging the culture solution 5 from theculture device 1. A plurality of gas inlet pipes 10 having many inletports bored in an upper surface of pipe are disposed on the uppersurface of the bottom portion 14, thus comprising part of the gasintroducing member 6. The gas supplied from the gas introducing member 6is most preferably air containing carbonic acid gas, but it may also beonly air.

An artificial light source 2 is set in an inside space of the insidesemispherical dome. The artificial light source 2 allows the microalgaeto proceed with the photosynthesis even in the case of the outdoorculture during the nighttime. Further, in the case of the indoorculture, the photosynthesis can be advanced with artificial lightsources set both outside and inside the culture device, and in this casethe depth or thickness of the culture solution can be increased, ifnecessary.

FIG. 2 schematically shows a state during the culture. Bubbles 12 of thegas discharged from the gas inlet pipes 10 into the culture solution 5move up in the culture solution 5 along the internal wall of the outsidesemispherical dome 8 because of their buoyancy. This upward motion ofthe bubbles 12 promotes upward motion of the culture solution, thecarbonic acid gas included in the bubbles 12 is supplied into theculture solution, and the oxygen evolving in the photosynthesis of themicroalgae is taken into the bubbles 12. The bubbles 12 are releasedinto the atmosphere at the surface of the culture solution. A stream 17of the culture solution moving up along the inner wall of the dome 8descends along the wall of the inside semispherical dome 9.

As described above, the gas of air etc. supplied from near the bottomportion into the culture solution functions to supply the carbonic acidgas into the culture solution and take in the evolving oxygen gas torelease it into the atmosphere on one hand and to uniformly agitate theculture solution on the other hand.

During the summer season, in which the culture can be hard because of arise of the temperature of the culture solution, the cooling water 15 issupplied from the water sprinkling member 3 onto the surface of theoutside semispherical dome 8, so as to control the temperature of theculture solution. The water used for the cooling is collected via thesprinkled water receiver 11 and is used again.

When in the outdoor culture the culture is also carried out during thenighttime, 24-hour continuous culture can be done by use of theartificial light source 2 disposed in the inside space of the insidesemispherical dome 9.

The microalgae, receiving the sunlight during the daytime, activelycarry out the photosynthesis to increase and also produce and store theuseful substances such as the proteins, polysaccharides, fatty acids,pigments, vitamins, and so on, whereas in the nighttime, suchphotosynthesis is not carried out and the substances synthesized duringthe daytime are used because of energy consumption of the microalgaethemselves; for example, in the summer season, the weight up to about20% of the cells of algae is lost in the extreme case, when comparedwith that during the daytime, thus causing large loss.

In order to prevent this loss, the artificial light source is used tocarry on the photosynthesis so as to compensate for the loss. Therefore,the artificial light source can be arranged to supply the quantity oflight enough for minimum photosynthesis, but no trouble will be causedeven if the photosynthesis more than that is carried out. The artificiallight source can be one selected, for example, from a fluorescent tube,an incandescent lamp, a halogen lamp, and so on.

In the case of the indoor culture the artificial light sources can beused both outside and inside the culture device 1. The use of theartificial light sources 2 in this way permits efficient, continuousculture for 24 hours.

For monitoring the culture conditions, it is necessary to always measurethe temperature, the liquid level, pH, and dissolved oxygen amount (DO)of the culture solution and keep each of numerical values of thesefactors within an optimum range. It is thus desirable to attach sensorsof these factors to the device, and they are preferably set through thecylindrical opening portion 4 at the top part or through either the dome8 or the dome 9 or through the both. If they are attached to the domethe device will become complicated and considerable labor and time willbe necessary for cleaning etc.; therefore, they are most preferably setthrough the cylindrical opening portion 4.

This culture device 1 of the domed shape can be constructed of anarbitrary combination of two types of semispherical domes havingrespective radii different from each other, and this structure permitschange in the volume of the space formed between the two domes andchange in the distance between the domes. This means that the amount ofthe culture solution and the thickness or depth of the culture solutioncan be set freely.

Further, the microalgae attach to the surfaces of the device in contactwith the culture solution and thus, for the removal and cleaning of thisattachment, the outside semispherical dome 8, out of the two types ofthe semispherical domes combined, is detached, so as to permit each ofthe domes to be cleaned; or the both domes can also be detached to becleaned at different locations.

For the semispherical domes, it is very convenient to employ anassembly, for example, of two components as the outside semisphericaldome. In either case, each of the two types of domes does not have to bean integrally molded member, but can be an assembly of plural moldedcomponents.

The shape of the semispherical domes can be any semisphere-like domeshape obtained by cutting a sphere at an arbitrary position, but themost preferable shape is approximately semispherical in terms of theutilization efficiency of light and reception of light.

The present invention also embraces modified spherical shapes includingan egg shape etc., in addition to the spherical shapes.

The size of the domes applicable is, for example, about 50 cm to about200 cm in diameter, and the culture device can be constructed byarbitrarily selecting a proper size according to the kind of microalgaeto be cultured, the culture conditions, and the culture purpose.

The spacing between the two types of domes can be set so as to obtainthe maximum photosynthesis efficiency, though depending upon the kind ofmicroalgae, the culture conditions, and the culture purpose. Normally,the spacing is preferably 2.5 cm to 10 cm and more preferably about 5cm.

The domed culture device 1 having the dome spacing of 5 cm wasconstructed of the outside semispherical dome 8 having the radius ofabout 50 cm and the inside semispherical dome having the radius of about45 cm, and the cylindrical opening portion 4 molded as a separate memberfrom the domes and having the diameter of 6 cm was provided at the toppart of the dome 8.

The microalgae, Spirulina Platencis, were cultured by the use of thisculture device, whereby the culture concentration of 10 to 20 g/literand the productivity of 2.0 to 5.0 g/liter/day were realized. On theother hand, in the case of the conventional culture pond method, theculture concentration is 0.3 to 0.5 g/liter and the productivity is 0.1to 0.2 g/liter/day. It was thus verified that the productivity wasenhanced to about ten times that of the conventional culture method.

It was also verified in the culture of Haematococcus Pluviaris producingastaxanthin of a red pigment that it was possible to produce algalbodies (biomasses) containing a high content of 4% to 8% of the pigment,astaxanthin, by high concentration culture in the culture concentrationof 5 g to 10 g/liter. The culture of Haematococcus Pluviaris producingthis red pigment was very difficult in the conventional culture pondmethod. Moreover, the high concentration culture of about 5 g to 10g/liter was also able to be carried out with the marine algae ofNannochloropsis Oculata. The maximum concentration by the conventionalmethod was 0.2 to 0.4 g/liter.

FIG. 4 shows a system in which a lot of closed outdoor culture devicesaccording to the present invention are placed and which can culture themicroalgae simultaneously and in volume. In the system, the microalgaeof the same kind may be put and cultured simultaneously in theindividual component devices or the microalgae of different kinds may beput and cultured separately in the individual devices. Each of thedevices is equipped with the various sensors so as to be able to controlthe culture conditions.

This structure is very effective because the various culture conditionsof the individual devices can be controlled independently even if themicroalgae of different kinds are cultured in the individual devices.

Further, even if the devices are arranged in rather dense relation, theutilization efficiency of light or the light-receiving area of light peroccupying area is large; thus the structure is very convenient andsuitable for volume culture and the productivity is very high.

FIG. 5 and FIG. 6 show the culture device 21 of the conical shape.

FIG. 6 is a front view of the culture device 21 of the conical shape, inwhich the cylindrical opening portion 24 is provided at the top part ofoutside conical peripheral wall 28 made of the transparent material, thesprinkled water member 23 for cooling the peripheral wall 28 is providedoutside this opening portion 24, the sprinkled water receiver 31 forreceiving the cooling water sprinkled from the water sprinkling member23 is provided at the lower part of the peripheral wall 28, and thedevice 21 is supported by a plurality of fixing members 36.

Further, the gas introducing member 26 and the discharging member 27 ofthe culture solution are attached to the bottom portion 34 of the device21.

FIG. 5 is a sectional view of the device 21. This device 21 is comprisedof the outside conical peripheral wall 28 of the transparent material,an inside conical peripheral wall 29 of the transparent material, andthe bottom portion 34 for connecting the lower ends of the twoperipheral walls. The cylindrical opening portion 24 is provided as aseparate member at the top part of the outside conical peripheral wall28 and the water sprinkling member 23 is provided outside the openingportion 24 so that the cooling water is sprinkled from this watersprinkling member 23 over the surface of the peripheral wall 28 to dropwith covering the surface of the peripheral wall 28 in the film formdown into the sprinkled water receiver 31. The temperature of theculture solution 25 is controlled by the cooling water.

Each of the peripheral wall 28, peripheral wall 29, bottom portion 34,cylindrical opening portion 24, and sprinkled water receiver 31 is madeof the transparent material such as the acrylic resin.

The cooling water from the sprinkled water receiver 31 is drained offthrough the drain member (not illustrated).

Attached to the bottom portion 34 are the gas introducing member 26 forsupplying air and/or carbonic acid gas into the culture solution 25 andthe discharging member 27 for discharging the culture solution 25 fromthe device 21. A plurality of gas inlet pipes 30 having a lot of gasinlet ports bored in the upper surface of pipe are provided on the uppersurface of the bottom portion 34, thus comprising part of the gasintroducing member 26. Further, the artificial light source 22 isprovided in the inside space of the peripheral wall 29, so that thephotosynthesis can be carried out continuously during the nighttime inthe outdoor culture.

FIG. 7 and FIG. 8 show the culture device 41 of the cylindrical shape.

FIG. 8 is a front view of the culture device 41 of the cylindricalshape, in which the cylindrical opening portion 44 is provided near thecentral part of an upper wall of outside cylindrical peripheral wall 48made of the transparent material and having the upper wall 57, the watersprinkling member 43 for cooling the upper wall 57 and peripheral wall48 is provided outside this opening portion 44, the sprinkled waterreceiver 51 for receiving the cooling water sprinkled from the watersprinkling member 43 is provided at the lower part of the peripheralwall 48, and the device 41 is supported by a plurality of fixing members56.

Further, the gas introducing member 46 and the discharging member 47 ofthe culture solution are attached to the bottom portion 54 of the device41.

FIG. 7 is a sectional view of the device 41. The device 41 is composedof the outside cylindrical peripheral wall 48 having the upper wall 57,an inside cylindrical peripheral wall 49 having an upper wall 58, andthe bottom portion 54 for connecting the lower ends of the twoperipheral walls. The cylindrical opening portion 44 is integrallyformed near the central part of the upper wall 57, and the watersprinkling member 43 is provided outside the opening portion 44 so thatthe cooling water is sprinkled from this sprinkling member 43 over theupper wall 57 to drop with covering the surface of the peripheral wall48 in the film form down to the sprinkled water receiver 51.

The temperature of the culture solution 45 can be controlled by thecooling water.

Each of the peripheral wall 48, peripheral wall 49, upper wall 57, upperwall 58, cylindrical opening portion 44, and sprinkled water receiver 51is made of the transparent material such as the acrylic resin.

The cooling water is drained off from the sprinkled water receiver 51through the drain member (not illustrated). Attached to the bottomportion 54 are the gas introducing member 46 for supplying the gas intothe culture solution and the discharging member 47 for discharging theculture solution 45 from the device 41. A plurality of gas inlet pipes50 having many gas inlet ports bored in the upper surface of pipe areprovided on the upper surface of the bottom portion 54, thus comprisingpart of the gas introducing member 46.

Further, the artificial light source 42 is provided in the inside spaceformed by the upper wall 58 and the peripheral wall 49, so as to permitthe photosynthesis during the nighttime.

FIG. 9 to FIG. 12 are a perspective view, a side view, a plan view, anda sectional view, respectively, of the gas discharge device 100, andFIG. 13 is an enlarged sectional view of a discharge nozzle of the gasdischarge device.

The gas discharge device 100 is comprised of rectangular base plates101, 101′ opposed to each other, a bubble guide member 102 of a -shapedcross section opening down, and a discharge nozzle 103, the bubble guidemember 102 being inclined with respect to upper surfaces 107, 107′ ofthe rectangular base plates and having an inclined wall 104 as an uppersurface and an upper wall 105 almost horizontally extending at the upperend thereof, the bubble guide member 102 also having side walls 106,106′ hanging down from the both side edges of the inclined wall 104 andupper wall 105, the lower ends of the two side walls 106, 106′ beingjoined to the upper surfaces 107, 107′ of the two rectangular baseplates 101, 101′. The both rectangular base plates are fixed to eachother by fixing members 108, 108′.

The discharge nozzle 103 is provided through a through hole 109 bored inthe lower part of the inclined wall 104 so as to be rotatable. Stoppers110, 110′ are located at opposed positions on either side of the throughhole 109 on the outer periphery of the nozzle 103 so as to prevent thenozzle 103 from slipping off the through hole 109.

In either type of the main body of the culture device, i.e., in eitherof the domed shape, the conical shape, and the cylindrical shape, theinside edge and outside edge of the bottom portion are thecircumferences of concentric circles and the bottom portion is thus of acircular shape obtained by cutting a central portion out of a disk. Inorder to permit easy movement on the bottom portion of the bored circleshape, the front and rear portions of the rectangular base plates 101,101′ are bent in the same direction as illustrated in FIG. 11.

An angle of inclination of the inclined wall 104 is preferably designedso as to be 45° to 60° with respect to the upper surfaces of therectangular base plates.

FIG. 14 is an explanatory drawing to show a state in which the gasdischarge device is discharging the gas into the culture solution.

The gas of air or air containing carbonic acid gas is supplied from agas supply device (not illustrated) provided separately from the culturedevice, through a gas inlet tube 111 to the discharge nozzle 103 and isthen discharged from the tip portion of the nozzle toward the bottomportion 112 of the culture device. The gas 113 discharged hits thebottom portion 112 and thereafter moves up in the form of bubbles 114inside the bubble guide member 102, i.e., along the inclined wall 104and upper wall 105 to be fed from the end of the upper wall 105 into theculture solution 115. The bubbles 114 thus fed move up in the solutionto be discharged to the atmosphere at the surface of the culturesolution. While the gas is in contact with the culture solution, theculture solution absorbs the carbonic acid gas, whereas the gas takes inthe oxygen evolving in the photosynthesis of algae and forming bubblesor being dissolved in the culture solution. The bubbles 114 also push upthe solution during the upward motion in the culture solution, therebycausing convection of the solution.

The gas and bubbles 114 discharged from the tip end of the dischargenozzle 103 bring about the buoyancy of the gas discharge device itselfand a thrust in the direction indicated by an arrow. This causes the gasdischarge device 100 to move in a floating state in the direction of thearrow. The device repeatedly performs such operation as to land on thebottom portion because of the weight of the device 100 after somemovement and then float to move ahead; this operation makes the culturesolution agitated heavily. This operation of the gas discharge device inthe culture solution is similar to the motion of a frog hopping ahead.

The members forming the gas discharge device 100 are normally made ofplastics, but many plastics themselves are considerably lightweight, inaddition to the buoyancy in the culture solution; therefore, they areeither those molded of a material obtained by adding a filler with alarge specific weight into a plastic material to add some weight,artificial-stone-like members formed in lamination by bonding stonepowder or filler powder to the rectangular base plates 101, 101′ withsynthetic resin such as the epoxy resin or the like, those obtained byforming the lower part of the rectangular base plates 101, 101′ of anartificial-stone-like material and forming the upper part of a plasticmaterial, or those permitting adjustment of the total weight of the gasdischarge device 100 by detachable arrangement of weights of metal suchas lead or the like at arbitrary positions on opposed surfaces of therectangular base plates 101, 101′; among them, the most preferablemembers are those permitting the adjustment of the total weight.

FIG. 15 is a sectional, explanatory view of a culture apparatus 150 as acombination of the culture device body 151 of the domed shape with thegas discharge device 100′ and FIG. 16 is a top plan view thereof, partlybroken.

Here, the culture device body 151 is comprised of an outsidesemispherical dome 153, an inside semispherical dome 152, and a bottomportion 154 for connecting the lower ends of the two domes, acylindrical opening portion 155 is provided at the top part of the dome153, and the description of the other members is omitted herein.

All of these members are made of the transparent material, which is, forexample, the acrylic resin.

The gas discharge device 100′ to which the gas inlet tube 157 isconnected is put through the cylindrical opening portion 155 of theculture device body 151 and placed on the bottom portion 154.

The gas inlet tube 157 is made of a material selected from polyurethane,silicone, synthetic rubber, and so on, and is in contact with thesurface of the inside semispherical dome 152.

While the gas of air or the like is supplied to the gas discharge device100′, this device 100′ advances in the moving direction of an arrow withhopping in the culture solution. On this occasion the culture solutionis agitated sufficiently by the discharged gas and the motion of the gasdischarge device.

Since the gas discharge device 100′ moves ahead on the bottom portion154 of the annular shape, the device 100′ circularly moves on the bottomportion 154 while the gas inlet tube 157 connected thereto rubs orcleans the surface of the inside semispherical dome 152, as illustratedin FIG. 16. Namely, the device 100′ performs the circular motion on thebottom portion 154 with the gas inlet tube 157 rubbing or cleaning thesurface of the dome 152. This means that the gas inlet tube 157 acts toprevent the algae from attaching to the surface and also clean thesurface.

Since the gas discharge device 100′ moves while agitating the culturesolution 156, the algae likely to form colonies, if present, will bebroken and again dispersed in the culture solution, so that the culturecan be carried out very efficiently.

On this occasion, the gas inlet tube is twisted, but the dischargenozzle is free to rotate as illustrated in FIG. 13; therefore, thedischarge nozzle rotates in the through hole to cancel the twist.

FIG. 17 is a sectional, explanatory view of a culture apparatus 160 as acombination of the gas discharge device 100″ with the culture devicebody 161 of the conical shape.

Here, the culture device body 161 is comprised of an outside conicalperipheral wall 163 of the transparent material, an inside conicalspherical wall 162 of the transparent material, and a bottom portion 164for connecting the lower ends of the two peripheral walls, and acylindrical opening portion 165 of the transparent material is providedat the top part of the peripheral wall 163. The description of the othermembers is omitted herein.

The gas discharge device 100″ to which the gas inlet tube 167 isconnected is put through the cylindrical opening portion 165 and isplaced on the bottom portion 164.

While the gas of air or the like is supplied to the gas discharge device100″, this device 100″ repeats the forward motion while hopping in theculture solution. This motion is just as described with the cultureapparatus of FIG. 15 and FIG. 16.

FIG. 18 is a sectional, explanatory view of a culture apparatus 170 as acombination of the gas discharge device 100′″ with the culture devicebody 171 of the cylindrical shape.

Here, the culture device body 171 is comprised of an outside cylindricalperipheral wall 173 having an upper wall of the transparent material, aninside cylindrical peripheral wall 172 having an upper wall of thetransparent material, and a bottom portion 174 for connecting the lowerends of the two peripheral walls, and a cylindrical opening portion 175of the transparent material is provided in the central part of the upperwall of the outside cylindrical peripheral wall 173. The description ofthe other members is omitted herein.

The gas discharge device 100′″ to which the gas inlet tube 177 isconnected is put through the cylindrical opening portion 175 and isplaced on the bottom portion 174.

While the gas of air or the like is supplied to the gas discharge device100′″, this device 100′″ repeats the forward motion while hopping in theculture solution. This motion is just as described with the cultureapparatus of FIG. 15 and FIG. 16.

FIG. 19 is a perspective view to show another embodiment of the gasdischarge device of the present invention.

This gas discharge device 200 is different from the structure of the gasdischarge device 100 illustrated in FIG. 9 in that one rectangular baseplate 201 out of the opposed rectangular base plates 201, 201′ isshorter than the other rectangular base plate 201′ and in that the frontend portion and rear end portion of the rectangular base plate 201 arenot bent, but is the same in the other respects. Numeral 202 designatesthe bubble guide member, 203 the discharge nozzle, 211 the gas inlettube, 201 and 201′ the rectangular base plates, 204 the inclined wall,205 the upper wall, 206 the side wall, 207 and 207′ the upper surfaces,and 208 and 208′ the fixing members.

Weights (not illustrated) as the weight adjusting means are detachablyattached to the rectangular base plates 201, 201′.

FIG. 20 is a perspective view to show a further embodiment of the gasdischarge device of the present invention.

This gas discharge device 300 is different from the structure of the gasdischarge device 100 illustrated in FIG. 9 in that the front end andrear end of both the opposed rectangular base plates 301, 301′ are notbent, but is the same in the other respects. Numeral 302 designates thebubble guide member, 303 the discharge nozzle, 311 the gas inlet tube,301 and 301′ the rectangular base plates, 304 the inclined wall, 305 theupper wall, 306 the side wall, 307 and 307′ the upper surfaces of therectangular base plates, and 308 and 308′ the fixing members.

Weights (not illustrated) as the weight adjusting means are detachablyattached to the rectangular base plates 301, 301′.

FIG. 21 is a perspective view to show yet another embodiment of the gasdischarge device of the present invention. FIG. 22 is a sectional viewalong the line X-X′ of the gas discharge device in FIG. 21.

This gas discharge device 400 is comprised of the opposed rectangularbase plates 401, 401′, the bubble guide member 402 of a dogleggedcontour in the inverse-U-shaped cross section opening down, and thedischarge nozzle 403 to which the gas inlet tube 411 is connected, thebubble guide member 402 being provided as inclined with respect to theupper surfaces 407, 407′ of the rectangular base plate portions andhaving the structure of the inverse-U-shaped cross section in which theupper end of the semicircular inclined wall 404 as an upper surfaceextends to form an upper wall 405 as keeping the semicircular shape andbeing bent almost horizontally and in which the both side walls(comprised of side wall 406 and the other side wall (not illustrated))hang down from the edges of the semicircular shape, the lower ends ofthe both side walls being joined to the upper surfaces 407, 407′ of therectangular base plates. The discharge nozzle 403 is set rotatablythrough the through hole 409 bored in the top part of the semicircularshape in the lower part of the inclined wall 404 of the bubble guidemember 402 of the inverse-U-shaped cross section and two stoppers 410,410′ are located on the outer peripheral part of the discharge nozzle403 at the opposed positions on either side of the through hole 409 soas to prevent the discharge nozzle from slipping off the through hole409.

The end formed by the upper wall 405 and the both side walls is open andthe rectangular base plates 401, 401′ are fixed to each other by thefixing members 408, 408′.

In this embodiment the two rectangular base plates are not bent at thefront end and at the rear end, but they may also be similarly used evenif they have such structure that the front end portion and rear endportion of the two rectangular base plates are bent in the samedirection or such structure that only one rectangular base plate is bentat the front end portion and/or at the rear end portion.

Weights (not illustrated) as the weight adjusting means are detachablyattached to the rectangular base plates 401, 401′.

Industrial Application

As described above, the culture devices, the gas discharge devices, orthe culture apparatus as a combination of the culture device with thegas discharge device according to the present invention are suitable forthe culture in high concentrations of microalgae and the culturesolution does not have to be mechanically agitated intentionally.Further, when the artificial light source is set in the inside space ofthe device, the 24-hour continuous culture can be effected outdoors, andin the indoor culture the light can be irradiated from the inside andoutside of the device, so as to realize continuous culture.

What is claimed is:
 1. A culture device of microalgae, said device beingone of either shape selected from a domed shape, a conical shape, and acylindrical shape, wherein the culture device of the domed shapecomprises an outside semispherical dome of a transparent material, aninside semispherical dome of a transparent material, and a bottomportion connecting lower ends of the two domes, a cylindrical openingportion is provided at top part of the outside semispherical dome, andan introducing member of air and/or carbonic acid gas and a dischargingmember of a culture solution are provided in the bottom portion, whereinthe culture device of the conical shape comprises an outside conicalperipheral wall of a transparent material, a transparent inside conicalperipheral wall, and a bottom portion connecting lower ends of the twoperipheral walls, a cylindrical opening portion is provided at top partof the outside conical peripheral wall, and an introducing member of airand/or carbonic acid gas and a discharging member of a culture solutionare provided in the bottom portion, or, wherein the culture device ofthe cylindrical shape comprises an outside cylindrical peripheral wallhaving an upper wall of a transparent material, an inside cylindricalperipheral wall having an upper wall a transparent material, and abottom portion connecting lower ends of the two peripheral walls, acylindrical opening portion is provided in central part of the upperwall of the outside cylindrical peripheral wall, and an introducingmember of air and/or carbonic acid gas and a discharging member of aculture solution are provided in the bottom portion.
 2. The culturedevice according to claim 1, wherein the shape of the culture device isthe domed shape.
 3. The culture device according to claim 1, wherein theshape of the culture device is the conical shape.
 4. The culture deviceaccording to claim 1, wherein the shape of the culture device is thecylindrical shape.
 5. The culture device according to claim 1, whereinthe transparent material is acrylic resin.
 6. The culture deviceaccording to claim 1, wherein a member for water sprinkling is furtherprovided outside the cylindrical opening portion and a sprinkled waterreceiver is further provided around the outside periphery of the bottomportion.
 7. The culture device according to claim 1, wherein anartificial light source is further provided in an inside space of theinside semispherical dome, the inside conical peripheral wall, or theinside cylindrical peripheral wall.
 8. A gas discharge device for use ina culture device of microalgae, the gas discharge device comprising twoopposed rectangular base plates, a bubble guide member of a -shapedcross section opening down, and a discharge nozzle, wherein the bubbleguide member is set as inclined with respect to upper surfaces of therectangular base plates, an inclined wall as an upper surface of thebubble guide member is bent at an upper end thereof to form an upperwall extending substantially horizontally, the bubble guide member hasside walls hanging down from both side edges of the inclined wall andthe upper wall, lower ends of the both side walls are joined to theupper surfaces of the rectangular base plates, and the discharge nozzleis rotatably mounted through a through hole bored in a lower portion ofthe inclined wall.
 9. A gas discharge device for use in a culturedevice, comprising two opposed rectangular base plates, a bubble guidemember of an inverse-U-shaped cross section opening down, and adischarge nozzle, wherein the bubble guide member is set as inclinedwith respect to upper surfaces of the rectangular base plates, an upperend of a semicircular inclined wall as an upper surface of the bubbleguide member is bent to form an upper wall extending substantiallyhorizontally as keeping the semicircular shape, the bubble guide memberhas side walls hanging down from both side edges of the inclined walland the upper wall, lower ends of the both side walls are joined to theupper surfaces of the rectangular base plates, and the discharge nozzleis rotatably mounted through a through hole bored in a lower portion ofthe inclined wall.
 10. The gas discharge device selected from claim 8 or9, wherein at least one of the two opposed rectangular base plates isbent in the same direction at a front end portion and/or at a rear endportion.
 11. The gas discharge device selected from claim 8 or 9,wherein at least one of the two opposed rectangular base plates isprovided with weight adjusting means.
 12. A microalgae culture apparatuscomprising a culture device body and a gas discharge device, wherein theculture device body is a culture device of a domed shape, a conicalshape, or a cylindrical shape, wherein the culture device of the domedshape comprises an outside semispherical dome of a transparent material,an inside semispherical dome of a transparent material, and a bottomportion connecting lower ends of the two domes, a cylindrical openingportion is provided at top part of the outside semispherical dome, and adischarging member of a culture solution are provided in the bottomportion, wherein the culture device of the conical shape comprises anoutside conical peripheral wall of a transparent material, a transparentinside conical peripheral wall, and a bottom portion connecting lowerends of the two peripheral walls, a cylindrical opening portion isprovided at top part of the outside conical peripheral wall, and adischarging member of a culture solution are provided in the bottomportion, or, wherein the culture device of the cylindrical shapecomprises an outside cylindrical peripheral wall having an upper wall ofa transparent material, an inside cylindrical peripheral wall having anupper wall of a transparent material, and a bottom portion connectinglower ends of the two peripheral walls, a cylindrical opening portion isprovided in central part of the upper wall of the outside cylindricalperipheral wall, and a discharging member of a culture solution areprovided in the bottom portion, wherein the gas discharge devicecomprises two opposed rectangular base plates, a bubble guide member ofa -shaped cross section or an inverse-U-shaped cross section openingdown, and a discharge nozzle, the bubble guide member is set as inclinedwith respect to upper surfaces of the rectangular base plates, aninclined wall as an upper surface of the bubble guide member is bent atan upper end thereof to form an upper wall extending substantiallyhorizontally, the bubble guide member has side walls hanging down fromboth side edges of the inclined wall and the upper wall, lower ends ofthe both side walls are joined respectively to the two upper surfaces ofthe rectangular base plates, and the discharge nozzle is rotatablymounted through a through hole bored in a lower portion of the inclinedwall.
 13. The culture apparatus according to claim 12, wherein thetransparent material of the culture device body is acrylic resin. 14.The culture apparatus according to claim 12, wherein an introducingmember of air and/or carbonic acid gas is further provided in the bottomportion of the culture device body.
 15. The culture apparatus accordingto claim 12, wherein the culture device body further comprises a watersprinkling member outside the cylindrical opening portion and asprinkled water receiver around the outside periphery of the bottomportion.
 16. The culture apparatus according to claim 12, wherein theculture device body further comprises an artificial light source in aninside space of the inside semispherical dome, the inside conicalperipheral wall, or the inside cylindrical peripheral wall.
 17. Theculture apparatus according to claim 12, wherein at least one of therectangular base plates of the gas discharge device is bent in the samedirection at a front end portion and/or at a rear end portion.
 18. Theculture apparatus according to claim 12, wherein at least one of the tworectangular base plates of the gas discharge device is provided withweight adjusting means.